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Originally Posted by z12358
I feel many people are not really familiar with what goes into designing a complex acoustic system such as the exhaust.
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I did some research on exhaust acoustics when my buddy John and I put together a very simple exhaust to try to shed some weight and get a little more volume. It did have mufflers but they were the straight-through type. We found it resonated very badly at right around the RPM you cruise at on the highway. He took it off after a few days. It wasn't very loud at all, except for at that resonant frequency- where it was unbearable.
What I found in my research is that the straight through mufflers generally work better at high frequencies, which explains why it wasn't that loud at redline. I also learned some fairly simple formulas that could be used to determine the length of an exhaust that would be needed to cancel such a resonance. I forget the exact numbers now, but it was something like 7 feet per side. We found some pictures of a Boxster muffler cut open, and we could see the path that the exhaust followed as it went through. Well I'll be darned if the path length for the stock muffler wasn't very close to what we had calculated. It uses chambers to route the flow back and forth to add length. I'm sure there's more to it than that. BUT, we still plan to hack together another exhaust as an experiment, and run the pipes left to right and back to get the length we calculated.
We also found some evidence that this would work on some Mustang forum. Some guys had used this formula to create a resonance canceling T-pipe or an exhaust pipe of a particular length, and had surprisingly good results.
Acoustics are certainly complex! But the application to a simple exhaust for a car might not be that bad.
Cheers,
Ken
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